Work is in progress to determine the nature and extent of lipid-protein interactions in the density lipoprotein as well as in lipoproteins reconstituted from apolipoproteins and synthetic lipids. The ability of specific apolipoproteins to bind binary mixtures of demyristoyl phosphotidyl choline/dipalmitoyl phosphotidylcholine and demyrestoyl phosphotidylcholine/distearoyl phosphatidylcholine are being investigated by kinetic studies; the properties of the resulting phospholipid-protein complexes are to be studied with respect to their size, homogeneity, composition, morphology, and stability to denaturation. The specific domains of apoproteins primary structure enclosed in lipid-protein interactions in high density lipoprotein are being investigated through the procedure of proteolytic cleavage of the intact particle. Lipid-bound peptide fragments will be isolated and the portion of primary structure from which they are derived will be determined. In this way, information on the structural requirements for protein-lipid interactions will be elucidated.